The present invention relates to an information recording apparatus for injecting an energy beam into a recording medium to form a mark different in physical properties from a non-mark portion to thereby record information and particularly to an optical disk device.
Currently, generally available optical disks may be roughly classified into magneto-optical disks of the type in which a recording film is heated to form marks by means of inversion magnetic domains on the recording film, and phase-change disks of the type in which the quantity of given energy beam at the time of heating is controlled to thereby change the cooling speed of a recording film to form marks by means of amorphous regions on the recording film. In order to attain improvement in information transfer speed of these optical disks at the time of recording/reproducing operation, there are a method of increasing recording linear density and a method of increasing the scanning speed of the recording medium scanned by a light spot. Examples of the method of increasing recording linear density may include a method of shrinking/shortening mark/space length and a method of shortening the time pitch of the change of mark/space length to thereby reduce the time span for detecting the mark edge position. In such a method of increasing recording linear density, however, the signal-to-noise ratio in a reproduced signal becomes a problem. Accordingly, in the present situation, it is impossible to expect great increase of the recording linear density.
For the purpose of forming minute marks accurately on an optical disk as a first prior art, JP-A-5-298737 (laid-open on Nov. 12, 1993) discloses a method in which a recording waveform corresponding to a mark forming period is constituted by a sequence of pulses corresponding to the mark length of a recording data sequence and the number and amplitude of pulses are controlled in accordance with the length of the recording data sequence. The recording waveform of the mark forming period is divided into two parts, namely, a heat part and a tail part. The two parts are generally different in pulse height from each other. Further, in a mark non-forming period of the recording waveform, a pause part is pre-positioned to thereby generate recording auxiliary pulses. In the above first prior art, it is said that heat diffusion from a preceding mark forming portion to a mark front edge position just after the mark forming portion can be compensated by the method of the first prior art regardless of the space length so that the mark width and the mark edge position can be controlled accurately. Here, the mark forming period is representative of or corresponds to a mark length in a recording data sequence, and is defined as a period from the leading edge of the first one of pulses having an energy level for supplying recording energy required for formation of a single mark, that is, pulses having such an energy level that any mark cannot be formed if the energy level is not generated, to the trailing edge of the last pulse, as shown in FIG. 3. Further, the mark non-forming period is representative of or corresponds to a space length in a recording data sequence, and is defined as a period except the mark forming period. The above definition is common to the whole description in this specification.
Further, as a second prior art, JP-A-8-7277 (laid-open on Jan. 12, 1996) discloses a method in which each recording data is decomposed into a plurality of basic elements different in length from each other so that one recording pulse corresponds to one element, and each recording data is formed as a series of independent recording marks recorded by corresponding element pulses. In the second prior art, it is said that not only the lowering of the reproduced signal level can be prevented but also recording can be performed stably also in a modulation system including long marks even if independent marks are recorded by the disclosed method. Further, it is said that increase of jitter in a reproduced signal after repetition of rewriting can be suppressed in a rewritable type recording medium.
Further, as a third prior art, JP-A-9-134525 (laid-open on Oct. 22, 1986) discloses a method in which the pulse width of succeeding heating pulses and succeeding cooling pulses is selected to be substantially equal to a recording channel clock period in the case where an even-number or odd-number mark length with respect to the recording channel clock period is recorded in a multi-pulse recording system using a head heating pulse, succeeding heating pulses, succeeding cooling pulses and a tail cooling pulse. In the third prior art reference, it is said that the cooling time of the recording medium can be secured sufficiently so that accurate edge position control can be made by the disclosed method.
As other prior art references as for waveform control, there are JP-A-55-139693 (laid-open on Oct. 31, 1980), JP-A-61-237233 (laid-open on Oct. 22, 1986), etc.